1. Field of the Invention
The present invention relates to a tape cassette which is optimally adapted for use in recording and/or reproducing apparatus. Specifically to a tape cassette wherein tape guide pins are press-fitted onto a cassette casing.
2. Description of the Prior Disclosure
Recently, there have been proposed and developed various magnetic tape cassettes to serve as an external data storage medium.
One such magnetic tape cassette has been disclosed in U.S. Pat. No. 4,198,013. This conventional tape cassette includes a pair of reels, namely a supply reel and a take-up reel, rotatably supported in the cassette casing. As is generally known, magnetic tape is wound on the pair of reels through a plurality of tape guide pins by which the travelling path of the tape is controlled in such a manner that the tape is wound on the reels at a predetermined contact angle. That is, the tape travelling path is defined by the upstanding guide pins, each arranged at a predetermined location on the cassette casing. As shown in FIG. 1, a conventional guide pin 90 is integrally formed with a tape contact section 90a, upper and lower flange sections 90b, and a press-fit section 90c extending from the bottom surface of the lower flange section. Each section 90a, 90b, or 90c has a specific, constant outer diameter. As seen in FIG. 1, the guide pin 90 is fixed on the cassette casing such that the press-fit section 90c is press-fitted onto the aluminum alloy lower half of the casing. Such guide pins are traditionally formed by lathe machining. The machining accuracy may be affected by various machining conditions, such as deflection of the workpiece, fluctuation in bite by a cutting tool, and fluctuation in lubrication by a cutting lubricant. For example, as shown in FIG. 2, the press-fit section 90c is often formed in a reverse taper fashion in which the outer diameter is gradually increased from its root connected to the bottom surface of the lower flange section 90b to its end. Therefore, the outer diameter a at the root is slightly smaller than that b at the end. If such a reverse tapered press-fit section of the guide pin is press-fitted into the lower half of the casing, the greatest outer diameter of end of the press-fit section 90c expands a preformed hole and forms a hole 33 slightly greater than a required outer diameter of hole, over the whole length of press-fit section 90c. As a result, after pressing, pressure occurring between the outer periphery of the press-fit section 90c and the inner periphery of the hole formed in the lower half of the cassette casing is decreased. Under these conditions, since the guide pin 90 is not press-fitted tightly enough into the lower half, the guide pin 90 may be easily removed from the lower half. Therefore, there is a possibility that the guide pins may dislodge due to external forces, such as vibration.
During press-fitting of a guide pin, a maximum impact with regard to the lower half occurs at the beginning of pressing. Specifically, since the end of the reverse tapered press-fit section 90c has a maximum outer diameter, the initial impact during pressing becomes excessively high, thereby resulting in deformation or damage to the lower half. Therefore, the flatness of the lower half may be compromised and as a result tape travel may become unstable. The above mentioned defect of a reverse-tapered press-fit section for a guide pin may also occur to some degree in a non-tapered, or straight press-fit section for a guide pin. If a reverse-tapered or straight press-fit section is press-fitted onto the lower half of a cassette without any preformed hole, the flatness of the lower half may be compromised to a greater degree, due to the excessively high, initial impact necessary during pressing and in addition such guide pins may also be dislodged relatively easily by external forces. Traditionally, such a guide pin is used in the lower half of a casing in such a manner as to directly guide magnetic tape on its cylindrical outer peripheral surface or to guide magnetic tape via a guide roller rotatably assembled therearound. In general, since the surfaces of such conventional guide pins are finished within a range of a maximum surface-roughness Rmax 0.5 to 0.8 .mu.m, there is a possibility that dust may be generated at the point of contact between the guide pins and the coated tape surface, resulting in so-called dropout error if the tape cassette is used for a relatively long time. In a guide pin employing the guide roller, since magnetic tape is guided by the outer peripheral surface of the guide roller, generation of the previously described dust is reduced. Such guide rollers may provide extremely smooth tape feed, however this makes tape tension control quite difficult.
Furthermore, in tape cassettes including such press-fitted guide pins, the lower half, receiving the guide pins, is made of electrically conductive material, such as aluminum alloy, as previously described. Therefore, were an user, charged with static electricity to touch the lower half of the casing of the tape cassette while loading the recording and/or reproducing apparatus for operation, static electricity may be discharged through the lower half of the cassette, through the cassette holder of the apparatus into the electrical control unit including logical circuits, resulting in error of logical circuits because of their low degree of tolerance to static electricity.